Bellringer:Write question and answer in complete

sentences

• What happens to a saturated solution if it is heated?

Chapter 22Solutions

Section 2October 22

Concentration

• Concentrated solution – large amount of solute

• Dilute solution – small amount of solute

Concentration

• % by Volume% by Volume– usu. liquid in liquid– EX: 10% juice = 10mL juice + 90mL water

• % by Mass% by Mass• usu. solid in liquid• EX: 20% NaCl = 20g NaCl + 80g

water

Precise Concentrations

• Concentrated and dilute are not precise terms. However, concentrations of solutions can be described precisely

• One way is to state the percentage by volume of the solute

Solubility

• Solubility–maximum grams of solute that will

dissolve in 100 g of solvent at a given temperature

– varies with temperature– based on a saturated solution

Comparing Solubilities

• The amount of a substance that can dissolve in a solvent depends on the nature of these substances.

• In one beaker, 1 g of solute A dissolves completely, but additional solute does not dissolve and falls to the bottom of the beaker.

Comparing Solubilities

• 1 g of solute B dissolves completely, and two more grams also dissolve before solute begins to fall to the bottom.

• If the temperature of the water is the same in both beakers; you

can conclude that substance B is more soluble than substance A.

Solubility Curves

• Each line on the graph is called a solubility curve for a particular substance.

• You can use a solubility curve to figure out how much solute will dissolve at any temperature given on the graph.

Types of Solutions–Saturated

• A saturated solution is a solution that contains all the solute it can hold at a given temperature

• This table shows the amounts of a few solutes that can dissolve in 100 g of water at different temperatures, forming saturated solutions.

Solubility

• Solids are more soluble at...–high temperatures.

• Gases are more soluble at......• low temperatures.• high pressures (Henry’s Law).

Concentration

SATURATED SOLUTIONno more solute

dissolves

SUPERSATURATED SOLUTION

becomes unstable,

crystals form

concentration

Unsaturated Solutions

• An unsaturated solution is any solution that can dissolve more solute at a given temperature

• Each time a saturated solution is heated to a higher temperature, it becomes unsaturated

Supersaturated Solutions

• A supersaturated solution is one that contains more solute than a saturated solution at the same temperature

• Supersaturated solutions are unstable.

Supersaturated Solutions

• For example, if a seed crystal of sodium acetate is dropped into the supersaturated solution, excess sodium acetate crystallizes out.

Solution Energy

• As the supersaturated solution of sodium acetate crystallizes, the solution becomes hot

• Energy is given off as new bonds form between the ions and the water molecules

Solution Energy

• Another result of solution energy is to reduce the temperature of the solution.

• Some substances, such as ammonium nitrate, must draw energy from the surroundings to dissolve.

• This is what happens when a cold pack is activated to treat minor injuries or to reduce swelling.

Solubility of Gases

• Shaking or pouring a solution of a gas in a liquid causes gas to come out of the solution.

• Agitating the solution exposes more gas molecules to the surface, where they escape from the liquid.

Pressure Effects

• Soft drinks are bottled under increased pressure

• When the pressure is released, the carbon dioxide bubbles out.

Temperature Effects

• Another way to increase the amount of gas that dissolves in a liquid is to cool the liquid

• This is just the opposite of what you do to increase the speed at which most solids dissolve in a liquid.